1. Field of the Invention
The present invention relates to a correction value retaining method in an engine control device for controlling the operational state of an engine according to a control variable obtained by detecting the operational state of the engine, finding a correction value to correct the control variable based on the control result of the operational state, and storing the correction value in a volatile memory.
2. Description of the Related Art
A well-known type of engine control device controls the operational state of an engine according to a control variable obtained by detecting the operational state of the engine, determines a correction value to correct the control variable based on the control result of the operational state, corrects the control variable according to the correction value by itself, stores the correction value in a volatile memory, and retains the stored correction value after the operation of the engine control device is stopped.
FIG. 1 is a schematic structural view of an engine control device according to the prior art. A correction value found by a CPU 1 is stored in a RAM 2. Electric power is supplied from a battery 6 to the CPU 1 through a power supply switch 5 and a power supply circuit 3. Electric power From the battery 6 is also supplied to the RAM 2 through a power supply circuit 4. In other words, the conventional engine control device is supplied with electric power from two circuits, and one of the circuits continuously supplies power to the RAM 2 even after the power supply switch 5 is turned off. Therefore, it is possible to retain the correction value stored in the RAM 2 after the operation of the engine control device is stopped and to reuse the correction value in the next operation.
However, since supply of electric power from two circuits is necessary in such a conventional correction value retaining method, the number of components of the engine control device is increased, and thus costs are also increased.
Furthermore, since power is still supplied to the engine control device while the engine control device is not in operation, it is feared that a battery may become flat due to discharge over a long period of time.
If the power supply is cut off while the operation is stopped, for example, if a battery is detached or the battery voltage falls, no voltage is supplied to the volatile memory, data in the volatile memory is destroyed, and the correction value is erased.
Furthermore, in order to enhance reliability of the correction value stored in the volatile memory on the assumption that the power supply will be cut off when the engine control device is not in operation, it is necessary to provide a means which can determine immediately after the start of an operation whether or not power was normally supplied while no operation was being performed.
As described above, the method of retaining a correction value in the volatile memory by supplying electric power while the engine control device is not operated is disadvantageous in cost and reliability.